1. Field of the Invention
The present invention relates to the measurement of battery capacity by correlation to equivalent internal resistance, and more particularly, to a circuit for indirectly determining the equivalent internal resistance of a battery by momentarily applying an RC load across the battery terminals and measuring the process of RC charging.
2. Description of the Background
One of the most accurate methods for determining battery capacity is by measuring the specific gravity of the electrolyte. Unfortunately, measurement of a battery's specific gravity is a complex and troublesome task. A more practical method is by measuring the equivalent internal resistance of the battery, i.e., determining the reduction in voltage supplied by the battery as a function of load. However, such voltage measurements are prone to great error. Moreover, measurement of a battery's internal resistance requires a complex electrometer which must be capable of applying various low resistance loads directly across the positive and negative terminals of the battery. This results in a great current drain to the battery which consumes power and induces sparking. The temperature of battery and cord rise to extreme temperatures. These conditions make it extremely dangerous for an inexperienced person to conduct the measurement.